Process and apparatus for eliminating impurities during the separation of gas mixtures



Oct. 28, 1952 E. F. YENDALL 2,615,312

PROCESS AND APPARATUS FOR ELIMINATING IMPURITIEIS DURING THE SEPARATION OF GAS MIXTURES Filed May 7, 1949 2 SHEETS-SHEET 1 NITROGEN INVENTOR 'EDWARD F. YENDALL ATTORNEY Oct. 28, 1952 E. F. YENDALL 2,615,312

PROCESS AND APPARATUS FOR ELIMINATING IMPURITIES DURING THE SEPARATION OF GAS MIXTURES 2 SHEETS-SHEET 2 Filed May '7, 1949 5% W mm a T N NY R w m M A m Wm NS my N Aw H 23052 0 fiu 5808 w\ Patented Oct. 28, 1952 PROCESS AND APPARATUS FOR ELIMINAT- ING IMPURITIES DURING THE SEPARA- TION OF GAS MIXTURES Edward F. YendalLKenmore, N. Y., assignor, by

mesneassignments, to Union Carbide and Carbon Corporation, a corporation of New York Application May 7, 1949, Serial No. 91,982

10 Claims.

1 This invention relates to the separation of components of gas mixtures and more especially it'concerns a process and apparatus for eliminating higher boiling point impurities such as carbon dioxide, hydrocarbons, et cetera, during the separation of gas mixtures such as air by low temperature rectification.

Heretofore, in the separation of air by low temperature rectification processes, difliculties normally have arisen as a result of the presence in the air of hydrocarbons and other impurities which tend to accumulate and become concentrated in portions of the rectification apparatus, and particularly in those portions of the apparatus where the oxygen is produced and isolated, at which points the presence of hydrocarbons constitutes a serious industrial hazard.

Various attempts have been made to minimize these hydrocarbon accumulations by separating such impurities from an intermediate crude liquid oxygen product, for example, by filtering the liquid being transferred from a higher pressure stage to a lower pressure stage of rectification. Another procedure involves'the use of an auxiliary condenser having a condensing head disposed within a vaporizing chamber, and having a condensate chamber at its lower end. The impurityfree vapors produced in the vaporizing chamber of the auxiliary condenser flow from the top of the latter to an intermediate part of a low pressure rectifying column. Periodically or continuously the accumulated hydrocarbons and other solid impurities are withdrawn from the auxiliary condenser through a suitable drain connection and discarded with a substantial amount of the valuable liquid. Nevertheless, the heat-exchange surfaces of the auxiliary condenser gradually collect carbon dioxide, hydrocarbons, and other solid impurities to an extent such that the heat transfer efficiency of the auxiliary condenser eventually is seriously impaired. Many impurities havesubstantial solubility in liquid air and oxygen so that filtration methods cannot be completely effective. Furthermore, the concentration of such impurities sometimes has resulted in these impurities being carried over in the vapors flowing to the rectifying column.

Among the more important objects of this invention are the following: to provide a novel process and apparatus for preventing or retarding the undue accumulation of hydrocarbons and other impurities in elements of a gas separation plant wherein concentration or rectification of components of gas mixtures is being conducted at low temperatures; to provide in novel manner for eliminating or reducing the loss in production capacity caused by the use in the usual manner of an auxiliary condenser in conjunction with rectifying apparatus; and to provide for accumulating hydrocarbons and other impurities within a zone external to and remote from the rectifying apparatus and auxiliary condenser, so as to minimize the damage and loss of production capacity in the event of flashing of such impurities in the presence of high purity oxygen.

In the practice of a preferred modification oi the invention for the separation of air, the latter is compressed and cooled in the usual manner while under pressure to a low temperature. 'A portion of the cooled air is liquefied upon expansion to a lower pressure. All of the cooled air preferably is. then thoroughly scrubbed with liquefied portions of the air ata lower pressure. The solid impurities are retained by the liquid fraction, and the substantially impurity-free gaseous fraction may be passed directly to the lower portion of a high pressure zone of a two-stage rectifying column. The liquid fraction of the air, which contains the solid impurities, may be filtered by passing it through one of a pair of duplicate filters. The solid carbon dioxide and hydrocarbons collect on the filters. The filtered liquid fraction then may be passed directly into a low pressure rectifying zone or column.' The aforesaid scrubbing of the air and the filtration of the liquid fraction of the scrubbed air may be dispensed with if desired, the cooled and partly liquefied air being then passed directly into a rectifying column.

The accumulation of hydrocarbons includin acetylene on a filter in liquid oxygen does not avoid completely the well-known hazard of hydrocarbon-oxygen mixtures. It has been discovered that the adsorption of hydrocarbons including acetylene in the fine pores of a adsorbent material that is inert to oxygen such as silica gel, alumina gel, or other mineral adsorbents is not hazardous but that the gel after it has adsorbed a considerable amount of these hydrocarbons and despite the presence of pure oxygen is not sensitive to flashing.

It is a distinguishing and important feature of the invention that a residual liquid rich in oxygen is withdrawn from a zone where liquid oxygen is collected and concentrated, is forced through a hydrocarbon removing device including a body of mineral adsorbent material and the cleaned liquid is passed to a vaporizing zone. A considerable amount of the dangerous impurities may be safely retained by the adsorbent before used for drying the air.

it is necessary to renew the adsorbent which is conveniently done by warming and evacuating or by purging with a relatively warm clean gas. According to another embodiment of the invention, a liquid intermediate product rich in oxygen is withdrawn from the lower portion of the rectification column or zone in which the main rectification occurs and is conducted to a storage reservoir from whence it is forced through an adsorbent device, or one of a pair of such devices,

by means of a suitable pump, thereby removing" gases of lower oxygen content from a rectifying column or a chamber operating under a higher pressure; The resultant oxygen vapors, free from impurities, are conducted to the condenser tubes of an auxiliary condenser, and there are condensed by heat exchange with a colder fluid,

preferably liquid oxygen withdrawn from the -main condenser andbeing vaporized, under. a

pressure about equal. to the pressure of the low pressure'rectifying column or zone with which 'the vaporizing chamber of the auxiliary condenser is in communication.

Thus it will .be understood that the pressure initiated at the pump is employed to facilitate operation of the auxiliary condenser evaporating compartment under a pressure approximately that of the low pressure rectifying column, while the maincondenser high purity oxygenevaporating compartment may be operated at somewhat higher pressures made possible by use of the The above-mentioned objects and features of the invention and other objects and advantages will become apparent from the following description in connection with the accompanying A drawings, in which: i

Fig; l is a diagrammatic View of an assemblage of apparatus embodying the principles of the inventionin a system for producing liquid oxygen 7 from air; and

Fig. 2 is a similar view of apparatus embodying principles of the invention in a system for producing gaseous oxygen.

For air separation by low temperature rectification, various cycles for the refrigeration and partial liquefaction of the air can be employed; and'any'of the customaryprocedures may be However, in the modification shown in Fig. l, the air entering the unit "may preferably be washed with water or cleaned by other customary means. The air then passes through conduit 14 into the low pressure cylinder of a multi-stage air compressor i5 wherein the airis compressed to a high pressure which -may be as much as 2000 pounds per square inch. The compressed air leaves the compressor through pipe l6 having therein an after cooler -ll,'and passes through the high pressure tube 2L, The air leaves the trap through conduit 22 having branch lines 23 and 28. Conduit 23 conducts a large portion of the air to the upper tube header 2'! of a main countercurrent heat exchanger 24. A conduit 25 having therein an expansionvalve 26 conducts the cold air containing particles of solid' carbon dioxide and the hydrocarbons and other impurities from heat exchanger is into the lower portion of a scrubber-separator 32. Expansion valve 26 may be used to reduce the-pressure of the air to that of scrubber 32 which may, for example, be substantially that existing in the high pressure stage of rectification or somewhat higher. A portion of the air expanded' through valve 2c is liquid at the pressure of scrubber 32.

Preferably a, substantial portion of the air leaving the trap 26 through line 22 is conducted through branch line 28 to an expansion engine 29 wherein the air is expanded to the'pressure of the scrubber 32 and, due to the production of external work, the temperature of the air is reduced to a very low value. The expanded airis then conducted to. the scrubber 32 through conduit30. p

The scrubber 32 is provided with gas and liquid contact means, which preferably comprise a series of perforated plates disposed above the inlet conduits 25' and '30 and extending upward for a short portion ofthe scrubber, leaving a large vapor space above the plates to prevent loss of liquid. by entrainment in'the-gases. An overflow chamber 34 maintains'the' liquid level slightly above the upper plate 33. 'lhegaseous fraction leaves the scrubber through-conduit Bit-and flows to the lower portion of. a "relatively. high pressure chamber 35: of a rectifying column -R,,which chamber may function under a pressure of around 100 pounds per square inch.

The liquid fraction containing solid carbon dioxide and hydrocarbon impurities in solid and dissolved state is conducted from the scrubber 32 through conduit 38 to one of a pair of filters 39, 39'. These filters conveniently may be similar to the filters i2, 33, described in United States Patent No. 2,337,474 of H. C. Kornemann and E. F. Yendall. Conduit 38 has two valvecontrolled branches 40, d0 connecting it with the filters.

The filtered liquid leaves the filters through the valved branch lines 4| and 4| and the main conduit 42 which conducts the filtered liquid to a mid-portion ofa. relatively low pressure chamber 4410f the rectifying column B, which chamber may function under a pressure around 6 to 8 pounds per square inch. 7

' The rectifyingcolumn R, in the form shown,

comprises a lower rectifying column 35 and an upper rectifying column 4s, each having customary gas and liquid contact trays d5. A main condenser 46 is located in a chamber 47 intermediate the upper and lower rectifying columns. The'chamber All and upper column 44 are not in direct unrestricted communication, being separated by a solid diaphragm such as the plate 48. The upper end of column 36 communicates with the interior of the tubes of condenser and th former has a liquid collecting shelf 49 disposed immediately below the condenser. The

oxygen evaporation chamber 41 surrounding condenser 46 may function under a pressure around 15 pounds per square inch.

Crude oxygen-containing liquid collecting at the lower end of column 35 is transferred by a conduit 50 controlled by a valve 51 to an intermediate portion of the upper column 44. Liquid .ent 68.

high in nitrogen collects at the shelf 49 and is transferred to the upper end of column 44 through conduit 52 controlled by a valve 53, to provide a further reflux liquid for that column.

The nitrogen product of the separation flows from the top of the upper column 44 through a conduit 54 to the lower end of main heat exchanger 24, and thence through the latter in countercurrent indirect heat exchange relation with the high pressure air in the exchanger tubes. The nitrogen leaves exchanger 24 through conduit 55 which conducts it to the lower end of heat exchanger I8. The nitrogen leaves the latter through conduit 56.

Except for the arrangement of the condenser chamber 41, the apparatus thus far described is similar to that disclosed in the aforesaid Patent No. 2,337,474. g

The impurity-containing oxygen-rich liquid collecting in the lower portion of the upper rectifying column 44 is withdrawn through conduit 58 and conducted to a reservoir 60 for the liquid. The lower portion of the reservoir 60 is connected through conduit 6| with the inlet of a liquid oxygen pump 62, which may be similar to that described in United States Patent No. 2,340,787 of G. H. Zenner and E. F. Yendall. The ump 62 forces the liquid through conduit 63 and branches 64, 64', controlled by valves '65, 65, into and through one of a pair of impurity removing devices 66, 66. The devices 66 and 66' may comprise tanks or chambers having transverse screens 61 near each end with the space between the screens packed with granular adsorb- The adsorbent material is preferably a mineraI gel having selective adsorbent capacity for the impurities. Silica and alumina gels have been found preferable and safe.

From the devices 66, 66, the cleaned liquid oxygen, now free from solid anddissolved impurities, is passed through a corresponding conduit 69, 69, controlled by one ofthe valve 16, and through line 1|, controlled byvalve 12,

' ing through the devices 66, 66' may be recycled into the lower portion of chamber 41. A portion of the cleaned oxygen is there vaporized, and is conducted through conduit 13 to the heat exchanger tubes 14 of an auxiliary condenser C,

where it is condensed and the high purity-liquid oxygen product withdrawn from the system through valve-controlled conduit 15.

The residual liquid oxygen is continously withdrawn from chamber 41 and conducted through conduit 16, controlled by valve 11, to the vaporizing compartment 16 of the auxiliary condenser C, where it is vaporized by heat exchange with the oxygen being condensed in condenser tubes 14-. The vapors from compartment 18 flow through conduit 19 to the lower portion of column 44. Any residual unvaporized liquid, which will retain any residual hydrocarbons and/or other impurities, may be conducted from the lower part of compartment 18, either continuously or intermittently, through a conduit 86, controlled by valve 8|, to the reservoir 60, and thence recirculated to one of the devices 66, 66.

Portions of the oxygen vapors formed in the evaporating chamber 41 are conducted through a valve-controlled conduit 82 connecting portions of conduits 13 and 19, into thelower end of the rectifying column 44.

Either device 66 or 66' may be purged of adsorbed impurities and any solid state impurities also retained, when desired, by closing valves 65,

1D, or 65', 16', and passing dry efliuent nitrogen which may have been previously heated, through a conduit 84 and one of respective valved branches 85, 85', intothe corresponding device 66. The nitrogen and gasifled impurities leave through a corresponding valved waste conduit 86 or 86'. Thus, if it is desired to thaw and regenerate the adsorbent in the device 66, valves 65 and 16 are closed, and valves 65, 16, 65 and 86 are opened. A stream of warm dry nitrogen then flows from conduit 84 to the interior of the device 66, through the adsorbent material 68 and then out through line 86. Substantially all of the impurities collected in the adsorbent are released and blown out. When the device 66' has been in service for a determined period, it may be regenerated in a similar manner.

By the use of the pump 62, and the proper adjustment of the valves 15, 11, 82, 5|, and 53, the evaporating chamber 41 may be operated at a pressure around 6 to 8 p. s. i. above the pressure in the upper column 44. Thus, oxygen is vaporized under pressure in chamber 41, and later is condensed in condenser 14, refrigeration for the purpose being supplied by the boiling of oxygen entering chamber 18 through conduit 16 and under the lower pressure of the column 44.

By regulation of a valve 81 in a drain conduit 88 from the bottom of chamber 41 to reservoir 60, any selected portion of the liquid passto insure that the liquid oxygen level in chamber 41 shall be maintained at the proper level for most eflicient heat transfer across condenser 46.

In certain instances it may be desirable to eiiect a preliminary removal of a large portion of the carbon dioxide of the air to be processed by chemical treatment of the air prior to or during compression and, in such instances, the scrubber-separator 32 and filters 39 and 39' may be omitted or by-passed by connecting conduits 25 and 30 directly to the lower column 36. No liquid fraction then flows to the upper chamber 44 but all the oxygen containing liquid collected in the high pressure chamber 36 is transferred to the upper chamber 44, for rectification therein, by conduit 50 and expansion valve 5|. The modification of Fig. 2 illustrates the principles of the invention as applied in a plant more specifically designed for the production of gaseous oxygen. As in Fig. 1, the apparatus for preparing the incoming air for entry into the rec- 'co'untercurrent heat exchanger I24.

A conduit I 25 conducts the compressed air which has been cooled to condensation temperature into the lower end of a scrubber separator I32. The conduit I25 has interposed therein an expansion valve I26. The other portion of compressed air flows through conduit I26 to an expansion engine I29 and the portion of air that is expanded with the production of external work is conducted from the engine through a conduit I36 to the lower part of the scrubberl32. The scrubber contains perforated plates I33 and an overflow cup I34 to maintain a liquid level just above the plates 133 so that the air is adequately scrubbed by liquid air as itpasses to the upper part of the. scrubber chamber I32. From the scrubber chamber a conduit I35 conducts the scrubbed air to the lower or high pressure chamber :36 of a two-stage rectifying column R.

A liquid overflowing into the cup I34, which contains solid carbon dioxide particles and some particles of hydrocarbon impurities, is conducted by a conduit I38 controlled by an expansion valve I31 to one of a pair of filters I39, I39. From the filters a conduit I42 conducts the filtered scrubber liquid to an intermediate point of an upper column I46 of the rectifying apparatus R.

The rectifying apparatus R comprises the high pressure chamber I36 and the upper low pressure rectifying chamber E44, which has at its lower end a vaporizing chamber I41, the chambers being separated by a main condenser I46 disposed inthe chamber I41. The main condenser receives vapor internally of its tubes from the chamber I36 and such vapor is condensed to form reflux for the chamber I36, so that a liquid enriched in oxygen is collected at the bottom of the chamber I36. Such liquid is transferred through a conduit'Iiifl-controlled by a transfer valve I5I to an intermediate point of the upper chamber I64, for example, by joining conduit I42. 1

An annular shelf I49 is arranged at the upper end of the chamber I36 to catch some of the liquid condensed by the condenser I46, which liquid is very rich in nitrogen and is conducted by a conduit I52 to the upper end of the chamber 44 to provide reflux for the upper end 'of the low pressure chamber. a transfer valve I53 in the conduit I 52. The effluent nitrogen vapor of the chamber I44 is conducted by a conduit I54 to a nitrogen passage I51 of heat exchanger I26 and from the .warm end of which a conduit I55 conducts the nitrogen to a nitrogen passage I58 in heat exchanger !I6, from the warm end of which a conduit I56 conducts the product nitrogen away.

The oxygen product collects in liquid state in the chamber I 41 and is boiled by condenser I46 This is regulated by to provide vapor for the rectifying chamber I44.

A large part of the concentrated product oxygen flows in liquid form through a conduit I16 having a control valve I11 into an auxiliary, vaporizing chamber96 to be substantially completely vaporized therein by a heat exchange coil or condenser 9| disposed in the lower part of the chamber 96. The oxygen product vapors withdrawn from the top of the chamber 96 pass through a conduit 92 to a jacket passage of heat exchanger I24 and from heat exchanger I24 through a conduit 93 to heat exchanger I I8, and from the latter heat exchanger through a conduit 94 to a place of use or collecting receiver for the product oxygen. It will be preferable to provide a vapor phase connection 95 between the chambers I41 and 90 to equalize pressure and permit flow of oxygen vapor in either direction according to the relative evaporation rates effected by condenser I46 and the heat exchange coil or condenser 91. The heat exchange coil or condenser 9| is preferably heated by condensing a vapor for a useful purpose. To this end a portion of the cold scrubbed air is conducted by a branch 96 of conduit I35 to the condenser 9| and liquid air produced by the withdrawalof liquid from the lower part of the chamber 96 through a conduit I86 controlled by a valve I8I. Such liquid may be collected in a vessel I66, from whence the liquid to be recirculated is conductedby conduit I6! to a pump I62, which forces out through a connection I63 to the lower end of an adsorbent chamber I66 that contains an adsorbent material I68 retained between perforated plates or screens I61. The cleaned recirculating liquid is returned to the chamber 96 from the upper end of the chamber I66 through a conduit I1I. Since it may be desirable to draw the liquid directly from the chamber I41, a conduit I88 has been provided which connects to the conduit I16 and is controlled by a valve I81 to conduct the liquid into the reservoir I66. If the reservoir I66 and the liquid space of the chamber 96 are made of sufficient size, it may be advantageous to employ only one adsorbing device I66 instead of duplicate adsorbers, as in Fig. l, and when the adsorbing device I66 is to be regenerated, valves I65 and I16 at the inlet and outlet thereof are closed and a valve 93 in a conduit 99 connecting conduits I63 and I'll may be opened and the liquid continued in circulation so that for a limited period of timethe concentration of impurities in the circulating liquid will not exceed a dangerous upper limit. For regenerating the adsorbent in chamber I 66 there is provided a connection 184 at the upper end which receives warmednitrogen from a heater I66 that in turn is supplied with dry nitrogen by a blower I6I connected to draw dry nitrogen from the conduit I56 by a conduit I62. A nitrogen which is blown through the adsorbent material I66 is exhausted to the atmosphere through the lower connection I86.

When liquid oxygen is flowed directly from chamber I41 to chamber 66 through conduit I16 it will be preferable to have the chambers at about the same level or the chamber 96 may be at a lower level. Where it is more convenient to have the chamber 66 higher than chamber I41 it will be preferable to keep valve I11 closed and pass all the liquid oxygen that is to-be vaporized in chamber 60 through conduit I88 under control of valve I81 and force it by pump I62 through adsorber I66 to chamber 96.

While solid particles of impurities will be trapped and retained in the devices 66 and I66, it may be advisable, especially in instances where the scrubber 32 or I32 and filters 39 and I39 are not used, to provide filters in addition to the adsorbers in the recirculating stream. Thus filters similar to the filters 39 may be interposed in the conduits 6I or 63 or I6I or I63. Such filters will serve to increase the time between regenerations of the adsorbent materials.

It will be seen therefore that the improved impurity separating arrangement according to the invention may be applied to various types of gas separation plants to avoid accumulation of 9. undesirable amounts of impurities in the rectifying apparatus and to prevent such impurities from appearing in the desired product of the separation. Such result is accomplished whether or not a preliminary separation of the impurities is practiced prior to rectification, or whether or not the rectification is effected in a single stage or in two stages. Any impurities that may reach the final rectification chamber are eliminated by filtering and adsorption to such a degree that accumulation of impurities on boiling surfaces is prevented and the vapor pressure of impurities other than those which are too volatile to cause trouble, is kept so low thatno measurable amount remains in the product oxygen.

The invention has been specifically described in connection with the separation of the components of air to produce oxygen and nitrogen. However, the principles thereof are not limited to such use, but are applicable to the low temperature separation of other gas mixtures containing carbon dioxide and/or hydrocarbons such, for example, as coke oven gases.

Obviously various modifications may be made without departing from the spirit of the invention as herein described and claimed.

What is claimed is:

1. A process for limiting the accumulation of hydrocarbon impurities in an oxygen-rich product in a system for low temperature separation of air that includes a zone in which said prodnot is collected and partially vaporized, which process comprises withdrawing liquid oxygen product from said zone; forcing such withdrawn liquid into intimate contact with an adsorbent material that is inert to oxygen and selectively retains hydrocarbon impurities including acetylene in a flash-safe manner; passing the withdrawn cleaned liquid to a separate vaporizing zone and subjecting it to vaporization therein; and recirculating a portion of the liquid from said separate vaporizing zone through said adsorbent material and back to said separate vaporizing zone.

2. In a process for eliminating impurities during the separation of air by low temperature rectification which includes the steps of separating compressed cooled air into a substantially impurity-free vapor fraction that is rectified under a condensation pressure, and a liquid fraction containing impurities partly in solidified state and partly in solution, which liquid fraction is filtered to remove solidified impurities and rectified under a relatively low pressure, and a portion of the liquid oxygen product in the latter rectification is subjected to partial vaporization to provide vapor for said rectification, the improvement which comprises subjecting the liquid oxygen product to a separate vaporizing operation that forms a residual liquid in which the dissolved impurities tend to concentrate; recycling a portion of such residual liquid from the vaporizing operation through an impurity-removal operation including an adsorbent medium which removes hydrocarbons including acetylene in a flash-safe manner, and returning the cleaned liquid to said vaporizing operation.

3. Apparatus for eliminating impurities during the separation of air by low temperature rectification which comprises an air rectifying device including high and low pressure column chambers and an oxygen vaporizing chamber with a condenser therein in heat exchange relation to vapors of said high pressure column, and means for transferring crude oxygen con- 10 taining hydrocarbon impurities from the high pressure column chamber to the' l'ow pressure column chamber; means for withdrawingliquid oxygen containing impurities from said low pressure chamber; an .au'x'iliaryvaporizing chamber connected to receive thewithdrawn liquid; means for withdrawing liquid from saidaux'iliary chamber; means for. returning cleaned liquid to said auxiliary chamber; and recirculating means including a liquid oxygen pump. and a chamber containing an adsorbent materiall' operatively connected betweensaid withdrawing means'and said returning means. I i

'4. Apparatus foreliminating impurities'during the separation of air by low temperature rectification which comprises an air rectifying de vice including high and low pressure column chambers and an oxygenvaporizing chamber with a condenser therein in heat exchangerelation to vapors of said high pressure column; and means for transferring crude oxygen containing hydrocarbon impurities from .thehigh pressure column chamber to the low pressure column chamber; means, for withdrawing liquid oxygen 1 containing impurities from said low pressure chamber; an auxiliary vaporizing chamber;

means for returning cleaned liquid to said auxiliary chamber; and circulating means including a liquid oxygen pump and a chamber containing an adsorbent material operatively connected between said withdrawing means and said returning means.

5. Apparatus according to claim 4 which includes means for draining a. portion of liquid from said auxiliary vaporizing chamber to the inlet side of said pump.

6. Apparatus for eliminating impurities during the separation of air by lowtemperature rectification which comprises an air rectifying device including high and low pressure column chambers and an oxygen vaporizing chamber with a condenser therein in heat exchange relation to vapors of said high pressure column, and means for transferring crude oxygen containing hydrocarbon impurities from the high pressure column chamber to the low pressure column chamber; means for withdrawing liquid oxygen containing impurities from said low pressure chamber; an auxiliary vaporizer connected to receive liquid from said oxygen vaporizing chamber; a liquid circuit including a liquid oxygen pump and a chamber of adsorbent material; means for drawing liquid from said auxiliary chamber to said liquid circuit; and means for delivering cleaned liquid from said circuit to said auxiliary vaporizer.

7. Apparatus according to claim 6.which includes means for heating the auxiliary vaporizer by condensing a portion of cold incoming air.

8. Apparatus according to claim 6 which includes means for draining liquid from the oxy- I containing impurities from said low pressure. chamber; an auxiliary vaporizing chamber con-' nected to receive the withdrawn liquid; means.

for withdrawing liquidfrom said auxiliary chamber; means for returning cleaned liquid t said auxiliary chamber; a chamber containing an adsorbent material; and means 'operatively connected for efiecting circulation of liquid oxygen from said withdrawal means, through said ad- 'sorbent material to said returning means.

10. In a process for eliminating impurities during the separation of air by low temperature rectification which includes the steps of cleaning compressed and cooled air by scrubbing it with a liquid fraction of the air, rectifying the cleaned air to produce an oxygen enriched product which is subjected to partial vaporization to provide vapor for the rectification, the improvement comprising subjecting the oxygen product to a separate vaporizing operation that forms a residual liquid in which "residual impurities tend to concentrate; recycling a portion of such residual liquid from the vaporizing operation through an impurity-removal operation including an adsorbent medium which removes hydrocarbons in- 12 eluding acetylene in a flash-safe manner, and returning the cleaned liquid to' said vaporizing operation. I

EDWARD F. YENDALL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. A PROCESS FOR LIMITING THE ACCUMULATION OF HYDROCARBON IMPURITIES IN AN OXYGEN-RICH PRODUCT IN A SYSTEM FOR LOW TEMPERATURE SEPARATION OF AIR THAT INCLUDES A ZONE IN WHICH SAID PRODUCT IS COLLECTED AND PARTIALLY VAPORIZED, WHICH PROCESS COMPRISES WITHDRAWING LIQUID OXYGEN PRODUCT FROM SAID ZONE; FORCING SUCH WITHDRAWN LIQUID INTO INTIMATE CONTACT WITH AN ADSORBENT MATERIAL THAT IS INERT TO OXYGEN AND SELECTIVELY RETAINS HYDROCARBON IMPURITIES INCLUDING ACETYLENE IN A FLASH-SAFE MANNER; PASSING THE WITHDRAWN CLEANED LIQUID TO A SEPARATE VAPORIZING ZONE AND SUBJECTING IT TO VAPORIZIATION THEREIN; AND RECIRCULATING A PORTION OF THE LIQUID FROM SAID SEPARATE VAPORIZING ZONE THROUGH SAID ADSORBENT MATERIAL AND BACK TO SAID SEPARATE VAPORIZING ZONE. 